Object detection system

ABSTRACT

An object detection system utilizing one or more thin, planar structured light patterns projected into a volume of interest, along with digital processing hardware and one or more electronic imagers looking into the volume of interest. Triangulation is used to determine the intersection of the structured light pattern with objects in the volume of interest. Applications include navigation and obstacle avoidance systems for autonomous vehicles (including agricultural vehicles and domestic robots), security systems, and pet training systems.

This application claims priority to provisional patent application No.60/463,525, filed Apr. 17, 2003.

FIELD OF THE INVENTION

The field of the invention relates range finders, collision avoidancesystems, automated object detection systems, optical proximitydetectors, and machine vision.

BACKGROUND OF THE INVENTION

As technology has advanced over the years, more and more automated meanshave been developed to do tasks which were originally accomplished byhuman beings. Indeed, automation and machinery have made possible theaccomplishment of many things which human beings could not do withoutautomation and machinery. At one level, tasks have been automated bymaking special-purpose machines and/or special-purpose software which doparticular tasks. At another level, machines and software have beendesigned which automate the running of other machines and software.

One of the frontiers of modern automation is the automation of taskswhich have traditionally relied on human visual perception. In anagricultural example, many tasks are currently accomplished by peoplerunning fairly complex mobile machines, where the job of the person hasoften been reduced to simply navigating the machine from place to placeand controlling the machine with simple controls to perform differenttasks.

Technology is currently being developed to automate many agriculturaltasks to an even higher level, by providing autonomous guidancemechanisms for automated machines, such that human beings will not needto be present for a large fraction of the time the machine is operating,including times when the autonomous machine is moving from one place toanother.

One of the major challenges facing the designers of autonomousagricultural machinery is the design of systems which allow autonomousmachinery to intelligently navigate from place to place in real-worldenvironments. When a human being navigates a machine from place toplace, the human being utilizes the ability to recognize patterns andobjects, such as roadways, intersections, and obstacles along a path,and respond appropriately.

If the physical environment through which an autonomous vehicle needs tonavigate is well-known and specified, an effective guidance system canbe far more economically designed. Unfortunately, unexpected changes tothe environment occur frequently in the real world. In an agriculturalenvironment, unexpected obstacles that might be encountered includeparked cars, tools and machinery left in the wrong place, barrels, andfallen branches.

The agricultural industry needs inexpensive, highly physically robustsystems for detecting obstacles in the path of autonomous vehicles. Itis an object of the present invention to provide a highly mechanicallyrobust, inexpensive obstacle detection system which is suited for use onautonomous agricultural machinery.

In a home automation example, it may be desirable for a domestic robotto be able to navigate within a home, avoiding obstacles such asfurniture, walls, plumbing fixtures, appliances, and people, andnegotiating stairs.

In another home automation example, it may be desirable for a domesticrobot to be able to perform a security function, such as monitoring aroom to detect intruders, or keeping pets off of counter tops orfurniture.

SUMMARY OF THE INVENTION

In one embodiment, the present invention uses a rugged, inexpensivelaser diode and a beam splitter to project a structured light pattern inthe form of an array of co-originating beams of light forward from thefront of in an autonomous vehicle at a downward angle, such that thebeams intersect the ground a known distance in front of the vehicle. Avideo camera which is not co-planer with the projected beam arrayobserves the intersection of the beam array with objects in theenvironment. The height of the beam spot images in the video imagevaries with distance of the intersected object from the autonomousvehicle. The forward-projected beams traverse the obstacle from bottomto top as the vehicle moves forward. Triangulation is used to measureboth the height and distance from the vehicle at which eachforward-projected beam intersects either the ground or an obstacle, sothat the vehicle can either maneuver around obstructions or stop beforecolliding with them.

The projected beams of light are modulated at a known frequency, and theobserved video images are synchronously demodulated to provide an imageinsensitive to ambient lighting conditions.

In a preferred embodiment, two (approximately spatially coincident)video cameras with partially overlapping fields of view are used to geta wider forward-looking field of view and/or better angular resolutionwhile still using standard commercial modules. The system has no movingparts and can operate reliably under significant shock and vibrationconditions.

In another embodiment, the present invention acts as a collisionavoidance alarm and/or automated emergency braking system on railedvehicles such as trains and subway cars.

In another embodiment, the present invention provides navigation aid toa self-navigating domestic robot. In this embodiment, the optical andelectronic apparatus affixed to an autonomous domestic robot. In thisand other embodiments used on autonomous vehicles, the present inventionmay incorporate dead-reckoning hardware and mapping software. In such anembodiment, the present invention allows an autonomous vehicle toinexpensively map out its environment high degree of accuracy. Deadreckoning means contemplated to be incorporated into the presentinvention includes ground-contact forms of dead reckoning such aswheels, and non-contact forms of dead reckoning such as GPS and opticalodometry, as described in co-pending patent application Ser. No.10/786,245, filed Feb. 24, 2004 by Sinclair et. al., which is herebyincorporated by reference.

In a preferred embodiment, subsequent to the initial mapping of theenvironment, the amount of processing power needed to detect changes tothat environment and re-map detected changes is significantly less thanthe amount of processing power needed to form the original map. Themajority of objects mapped (such as walls, furniture, plumbing fixtures,and appliances will rarely move and thus rarely need to be re-mapped,whereas the position of doors, kitchen and dining room chairs, etc. maymove frequently. This efficient utilization of computational resourcesinherent in partial dynamic re-mapping can allow for lower powerconsumption and cheaper implementation of domestic robots. In addition,utilization of dead-reckoning systems in conjunction with objectdetection can result in far more computationally efficient navigationonce an area or operation has been initially mapped.

In another embodiment, the present invention uses multiple structuredlight patterns projected from a fixed position to measure changes inobject positions within a pre-determined “keep-out” volume of space overtime. In this embodiment, a training mode is provided in which thepresent invention learns the perimeter of the keep-out volume as anobject is three-dimensionally moved around the imaginary surface whichdefines the keep-out volume. One specifically contemplated applicationfor such an embodiment is use in security systems. Another applicationspecifically contemplated is domestic use to train pets to stay off oraway from cherished objects and furniture.

It is an object of the present invention to provide a mechanicallyrobust, inexpensive method and apparatus for obstacle detection for useon autonomous vehicles. It is a further object of the present inventionto provide an inexpensive optical security device capable of detectingunwanted movement or presence of objects within a monitored volume ofspace. It is a further object of the present invention to provide aninexpensive, mechanically robust, reliable vehicle collision avoidancesystem. It is a further object of the present invention to facilitateinexpensive self-navigating domestic robots.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-19 depict one out-of-plane camera's view of two non-coincidentplanes of co-originating beams of light intersecting with the ground andobstacles in the path of an autonomous vehicle.

FIG. 19 Depicts a side view of the mounting and orientation of twoplanar sets of co-originating light beams and two out-of-planeforward-looking video cameras on an autonomous vehicle.

FIG. 20 depicts a perspective view of an autonomous vehicle with twoprojected co-originating separately co-planar sets of beams of lightemitted and a video camera mounted non-coincident with either plane oflight beams.

FIG. 21 depicts a top view and a side view of a forward-pointeddownward-angled light beam emanating from the front of an autonomousvehicle, and shows how the position of the image of the projected lightbeam varies in the field of view of a video camera, according to thedistance and height of the point of intersection of the light beam withan obstacle.

FIGS. 22A and 22B depict side and top views of asingle-projection-aperture, single-imager implementation of the presentinvention.

FIGS. 22C and 22D depict mapping of object angular and radial positionto images acquired through normal and anamorphic lenses, respectively.

FIGS. 22E and 22F depict multiple-planar-structured-light-patternsingle-projection-aperture single-imager embodiments of the presentinvention.

FIG. 22G depicts a multiple-co-planar-structured-light-patternmultiple-projection-aperture single-co-planar-imager embodiment of thepresent invention.

FIG. 22H depicts a multiple-co-planar-imagersingle-coplanar-structured-light-pattern embodiment of the presentinvention.

DETAILED DESCRIPTIONS OF SOME PREFERRED EMBODIMENTS

In FIG. 21 an autonomous vehicle 2100 is equipped with the presentinvention. Forward-looking downward-angled light beam 2102 is emittedfrom beam source 2101. Light beam 2102 vertically traverses the field ofview of forward-looking video camera 2109. If light beam 2102 intersectssome object at distance D1 (from the front of autonomous vehicle 2100)and height H1, a spot 2110 is seen in the field of view of camera 2109.If light beam 2102 intersects some object tat distance D2 and height H2,a spot 2111 is seen in the field of view of camera 2109. If light beam2102 intersects some object at distance D3 and height H3, a spot 2112 isseen in the field of view of camera 2109. If light beam 2102 intersectssome object at distance D4 and height H4, a spot 2113 is seen in thefield of view of camera 2109. If light beam 2102 intersects the groundat distance D6 from the front of autonomous vehicle 2100, a spot 2114 isseen in the field of view of camera 2109.

Video camera 2109 views any object intersecting light beam 2102 atdistance D1 along line of site 2103. Video camera 2109 views any objectintersecting light beam 2102 at distance D2 along line of site 2104.Video camera 2109 views any object intersecting light beam 2102 atdistance D3 along line of site 2105. Video camera 2109 views any objectintersecting light beam 2102 at distance D4 along line of site 2106.Video camera 2109 views the ground intersecting light beam 2102 atdistance D5 along line of site 2107.

As autonomous vehicle 2100 moves forward an obstacle in its path wouldfirst be illuminated by light beam 2102 at distance D6 in front of thevehicle. As the vehicle moves closer to the object the illumination spotwhich light beam 2102 projects on the obstacle traverses the obstaclevertically from bottom to top. While FIG. 21 shows only one forwardprojected light beam, a preferred embodiment of the present inventionutilizes a beam splitter to project numerous co-originating coplanarbeams of light in a forward-looking downward-angled manner.

FIG. 19 illustrates a top view of a preferred embodiment of the presentinvention which projects three sets of light beams forward of theautonomous vehicle where each set of light beams is projected in adifferent plane and a different downward angle. As shown in FIG. 19, twosets of optics according to the present invention (each consisting of 3planar sets of light beams and an observation video camera) may be usedin a partially overlapping configuration to widen the forward-lookingviewing angle of the optical system. In an alternate embodiment, onlyone set of beam-projecting optics is used, and multiple video cameraswith partially overlapping fields of view are used to observe theintersection of the projected light beams with objects in theenvironment.

In a preferred embodiment of the present invention which utilizesmultiple sets of light beams intersecting the ground at progressivelyfurther distances from the autonomous vehicle (as illustrated in FIG.19), light beams projected further into the distance are projected withmore optical power than light beams projected closer to the autonomousvehicle. In a preferred embodiment of the present invention, eachcoplanar, co-originating set of light beams is derived by passing thebeam from a laser diode through a beam splitter.

FIGS. 1-19 depict one out-of-plane camera's view of two non-coincidentplanes of co-originating beams of light intersecting with the ground andobstacles in the path of an autonomous vehicle as the vehicle movesforward progressively. It can be seen from the figures that if the lightbeams are highly focused and non-overlapping, sometimes a thin objectmay fall between adjacent light beams. In a preferred embodiment of thepresent invention, there is some horizontal overlap between theprojected beams, forming almost a horizontal curtain of light, so thateven thin vertical objects will always intersect the projected lightpattern.

As the autonomous vehicle moves forward, the observed intersection ofnon-centrally projected beams not only traverses objects vertically asthe vehicle moves forward, the image also traverses intersected objectshorizontally. In one preferred embodiment, non-centrally-directedprojected split beams are tightly focused to improve signal-to-noiseratio, and non-centrally located thin objects are detected by observingthe image often enough so that the image of a spot traversing any objecthorizontally will always be observed. In such an embodiment, centrallylocated beams are given some overlap to avoid missing thinvertically-oriented centrally located objects which could otherwise bemissed (because there is no apparent “sideways” motion of centrallyprojected beams across the field of view of the video camera as the beamtraverses an obstacle due to forward motion of the vehicle.

In order to reduce sensitivity to ambient lighting conditions, in apreferred embodiment of the present invention, the projected light beamsare modulated and the observed video signal is synchronouslydemodulated. Since the video image is inherently sampled at the framerate of the video, it is convenient to phase-lock the modulation of theprojected light beams with the video sampling rate. For example, if thevideo sampling rate is 60 frames per second, a preferred embodiment ofthe present invention utilizes light beams that aresquare-wave-modulated at 30 Hz, such that the square-wave transitions inthe beam intensity occur simultaneously with the time boundaries betweensuccessive video captures. In such an embodiment, the beam pattern couldbe said to be present in every even numbered video capture, and absentin every odd numbered video capture. By taking the difference betweensuccessive video captures (or multiplying the brightness of each pixelsuccessively by +1 and −1) and averaging the result, the intersectionsof the projected beams with objects in the environment stand out in highcontrast to the remainder of the image.

It is important to keep dirt from getting on the optics of the system,and for sytems operating in an agricultural environment (which isreplete with sources of dirt, mist, chemicals, etc.), to prevent theoptics from accumulating dirt or liquid or chemical coatings which couldimpair performance, in a preferred embodiment of the present invention,the beam projecting and video optics are recessed in open-windowchambers which are connected to a positive-pressure air supply. Theoptics thus “looks out” through an opening which always has air flowingout through it, at a rate sufficient to prevent most dirt particles,moisture, chemicals, etc. from coming in contact with the optics. In analternate preferred embodiment, a rotating window may be used inconjunction with affixed sprayer and wiper to keep dirt out ofcontinuously used optics. In an alternate preferred embodiment, anautomatic intermittent sprayer and an automatic intermittent wiper maybe used to keep dirt out of the optics where the optics areintermittently used.

It is contemplated that alternate embodiments of the present inventioncould use beam scanning technology (such as the spinning mirrortechnology used in laser printers and check-out counter bar-codereaders). In embodiments of the present invention utilizing scanningoptics in place of a beam splitter, the advantage of continuous opticalstriping in captured images (which avoids missing “thin” objects insingle images) can be traded off against the advantages of reflectedoptical power inherent in projecting spots instead of stripes.

In determining the position of objects, the fundamental principal onwhich the present invention relies is triangulation. Some methods ofusing structured light in conjunction with one or more electronicimagers to perform triangulation are described above. Other methodscontemplated include projecting multiple simultaneous structured lightpatterns of different colors, multiple spatially interspersed andspatially distinguishable structured light patterns, and multipletemporally distinguishable structured light patterns. For instance theangle of a planar structured light pattern over time, between capturinga plurality of images. This embodiment may be particularly useful inapplications where the structured light projector and imager remainfixed and it is desired to monitor object movement within a volume ofspace over time, such as security applications or pet-trainingapplications. The triangulation of the present invention may beaccomplished with a single imager and a single projecting aperture,multiple imagers and a single projecting aperture, multiple projectingapertures and a single imager, or multiple projecting apertures andmultiple imagers.

Some varied embodiments of the present invention are depicted in FIGS.22A through 22G. FIG. 22A depicts a side view of a single-projectingaperture, single-imager embodiment of the present invention, analogousto the embodiment described above for use on autonomous vehicles. A thinplanar structured light pattern 2201 is projected forward of platform2200 through small aperture 2205 at angle 2204 from the horizontal.Imager 2206 images the intersection of structured light pattern 2201with any objects in its field of view. The top boundary and bottomboundary of the field of view of imager 2206 are indicated by dottedlines 2203 and 2202.

FIG. 22B depicts a side view of the same apparatus shown in FIG. 22A.Dotted lines 2208 and 2209 indicate the right and left boundaries of thefield of view of imager 2206. In one embodiment, the multiple lightbeams of structured light pattern 2201 may be produced simultaneously bypassing a laser through a beam splitter. In another embodiment, themultiple light beams of light pattern 2201 may be produced sequentiallyin time by scanning a laser (for instance, using a servo-driven rotatingmirror or prism).

FIG. 22C depicts the field of view 2214 of imager 2206. The locus ofpossible intersections of objects within the field of view with lightbeams 2210 and 2211 are indicated by line segments 2210A and 2211A,respectively. Thus it can be seen that in this depicted embodiment, thefield of view may usefully be divided into vertical stripes, which maponto different (left-to-right) angular positions in the field of view.Thus, light spots found within stripe 2218 would come from beam 2211intersecting objects in the field of view, while light spots foundwithin stripe 2219 would indicate objects intersecting light beam 2210.

It may also be seen that the vertical position of light spots foundwithin image boundaries 2214 is indicative of the radial distance ofthose objects from imager 2206. Thus, light spots found at height 2212within image frame 2214 would come from intersections of light beams witobjects at distance D1, while light spots found at height 2213 withinimage frame 2214 would come from intersections of light beams withobjects at distance D2.

In some preferred embodiments, it may be desirable to gain enhanceddistance resolution around some distance in the field of view. With theembodiment depicted in FIGS. 22A through 22D, this may be accomplishedusing an anamorphic lens. Utilizing an anamorphic lens which has morevertical magnification than horizontal magnification, field of view 2214shown in FIG. 22C is transformed into field of view 2215 shown in FIG.22D. Thus field of view 2215 images only intersections of objectsbetween distance D1 and distance D2 from imager 2206, while maintainingthe same left-to-right angular view as image 2214 in FIG. 22C.

It may be desirable in some applications of the present invention tohave the ability to detect objects within a three-dimensional volume,rather than just detecting the intersection of objects with atwo-dimensional structured light pattern. This may be accomplishedthrough detecting the intersection of objects with multiple planarstructured light patterns, where the planes of the multiple patterns areoriented at different angles, as shown in FIG. 22E. In FIG. 22E, a sideview of planar structured light patterns 2216, 2217, and 2201 are shown.Distinguishing these multiple structured light patterns in a singleimage may be accomplished several ways. In one embodiment,differentiation of multiple simultaneously projected structured lightpatterns is accomplished through the use of color. In such anembodiment, structured light patterns 2201, 2216, and 2217 are eachprojected using a different color.

In an alternate embodiment, left-to-right angular resolution is tradedoff against vertical resolution. In such an embodiment, the beams of themultiple planar structured light patterns are horizontally interlaced asshown in FIG. 22F.

In an alternate embodiment where objects in the field of view can beassumed to remain relatively still over some short period of time,multiple planar structured light patterns of differing angles may beprojected sequentially in time.

Although the preferred embodiments depicted in FIGS. 22A through 22Fabove utilize a single projection aperture for the structures lightpatterns, where that projection aperture is placed co-planer with theimager in a plane perpendicular to the plane of the projected structuredlight patterns, it should be noted that other geometries are possible.For instance, multiple projection apertures may be placed at differentpositions within a plane perpendicular to the projected light patternplanes, and the convenient mapping of horizontal in the acquired imageto left-right angle in space, and the convenient mapping of vertical inthe acquired image to radial distance from the imager will both still bemaintained. Other geometries with less convenient mappings are alsopossible.

FIG. 22G depicts a top view of amultiple-co-planar-structured-light-pattern multiple-projection-aperturesingle-co-planar-imager embodiment of the present invention. Twostructures light projection apertures and an imager could all be placedco-planer with two projected planer projected structured light patterns,and distance information would be extracted by comparing which lightbeams from each pattern intersected a given object at a given point. Insuch an embodiment, the two structured light patterns could be projectedsimultaneously in different colors, or sequentially in time. Since it isdesired in such an implementation to guarantee that each objectintersected by the first structures light pattern is also intersected bythe second structured light pattern, it may be desirable in such anembodiment to use swept-single-beam structured light patterns ratherthan beam-splitter-derived structures light patterns. Such an embodimentcan utilize a linear imager rather than a rectangular imager if onlytwo-dimensional sensing is to be done, or a two-dimensional imagingarray may be used if multiple planar projection angles are to be usedsimultaneously or over time.

A top view of a multiple-co-planar-imagersingle-coplanar-structured-light-pattern embodiment of the presentinvention is depicted in FIG. 22H. Such an embodiment does triangulationin the same way that normal stereo vision does triangulation, and thestructured light pattern provides a pattern to recognize which isindependent of lighting conditions. Such an embodiment can utilize alinear imager rather than a rectangular imager if only two-dimensionalsensing is to be done, or a two-dimensional imaging array may be used ifmultiple planar projection angles are to be used simultaneously or overtime.

In a preferred embodiment of the present invention, processing ofmultiple images is used in place of processing of a single image, toimprove signal-to-noise ratio through averaging techniques, andtechniques or removing from a set of images to be averaged any imagewith significantly outlying data. In a domestic application,statistically outlying images might be acquired when a flying insectflew near the optical aperture from which the structured light patternoriginates. In an agricultural application, a statistically outlyingimage might be acquired when debris blows in front of the structureslight source aperture, or when dirt or liquid momentarily corrupts thesurface of the optical aperture before being automatically removed.

In a preferred embodiment of the present invention, the re-locating ofobjects from various vantage points at various distances is used in themapping process to build an object map with more consistent spatialaccuracy than would be possible in mapping from a single vantage point.Since the error in triangulation is angular, the absolute distanceresolution gets linearly worse with radial distance from the imager.Imaging from multiple vantage points at a plurality of distancesovercomes this limitation.

In a preferred embodiment of the present invention, object mapping isdone utilizing varying spatial resolution, such that objects with largeapproximately planar surfaces are represented with few data points andobjects with more rapidly spatially varying features are representedwith more data points. In a preferred embodiment, the re-mapping of theposition of known objects is done in such a way that the most rapidlyspatially varying portions of objects that have moved take morecomputation time to re-map, while the less rapidly spatially varyingportions of objects take less time to re-map. This mapping architectureinherently represents the edges of objects with greatest accuracy, aswould be desired for navigation purposes.

The storage means used to store map data and image data in the presentinvention may be any type of computer memory such as magnetic disk, RAM,Flash EEROM, optical disk, magnetic tape, and any other type of memoryas may come into use over time for computational purposes. The means fordigitally processing acquired images in the present invention can be anytype of microprocessor, computer, digital signal processor, arrayprocessor, custom application-specific integrated circuit (ASIC), statemachine, or the like. The electronic imagers used in the presentinvention may be any type of electronic camera, video camera, liner ortwo-dimensional imaging array such as a CCD array, COMS array, or thelike.

The foregoing discussion should be understood as illustrative and shouldnot be considered to be limiting in any sense. While this invention hasbeen particularly shown and described with references to preferredembodiments thereof, it will be understood by those skilled in the artthat various changes in form and details may be made therein withoutdeparting from the spirit and scope of the invention as defined by theclaims.

1. An object detection system, comprising: A structured light sourcecapable of projecting a first pattern of structured light from a smallaperture, said first pattern of structured light falling within a thinplanar volume of space: A first electronic imager not co-planar withsaid first pattern of structured light, said imager arranged in apre-determined spatial relationship to said aperture, and said imagerimaging a region of space in which objects could intersect said firstprojected pattern of structured light; Means for storing at least oneelectronic images; and Means calculating object positions from thepositions in which structured light appears in a plurality of images. 2.The object detection system of claim 1, further comprising means forperforming dead reckoning, said dead reckoning means arranged in apre-determined spatial relationship to said aperture.
 3. The objectdetection system of claim 1, further comprising means for storing objectmap information about positions of detected objects.
 4. The objectdetection system of claim 1, further comprising means for indicating analarm condition if objects enter a volume of space where objects shouldnot be allowed.
 5. The object detection system of claim 1, furthercomprising means for taking automated corrective action if objects entera volume of space where objects should not be allowed.
 6. An objectdetection method, comprising: Projecting through a first small aperturea first structured light pattern within a first thin planar volume ofspace in which it is desired to measure the position of objects;Capturing and storing at least one image from a first electronic imagerpositioned in a predetermined spatial relationship to said first smallaperture; Digitally processing at least one captured image to determinepositions of objects intersecting said first structured light pattern.7. The method of claim 6, wherein said step of capturing at least oneelectronic image comprises capturing a plurality of images and furthercomprising the step of moving said electronic imager relative to saidobjects between capturing at least two of said plurality of images,while maintaining the spatial relationship between said first electronicimager and said first optical aperture.
 8. The method of claim 6,wherein said step of capturing at least one electronic image comprisescapturing a plurality of images, through a plurality of spatiallysubstantially non-coincident electronic imagers.
 9. The method of claim6, wherein said step of capturing at least one electronic imagecomprises capturing a plurality of images through said first electronicimager, and wherein said step of digitally processing at least onecaptured image comprises processing a plurality of captured images insuch a way as to improve signal to noise ratio, and spatial resolution.10. The method of claim 6, wherein said step of capturing at least oneelectronic image comprises capturing a plurality of images through saidfirst electronic imager, and varying the plane of said structured lightpattern between capturing at least two of said plurality of images suchthat images are captured of objects intersecting a plurality of thinplaner structured light patterns, and said step of digitally processingat least one captured image comprises processing a said plurality ofimages captured of intersections of objects with said plurality ofvaried-plane structured light patterns, to derive a three-dimensionalrepresentation of the intersection of objects with said plurality ofplanar structured light patterns.
 11. The method of claim 7, furthercomprising combining dead-reckoning data with object position data froma plurality of electronic images captured from a plurality of positionsof said electronic imager, to produce a three-dimensional representationof objects within a volume of interest.
 12. The method of claim 10,further comprising combining dead-reckoning data with redundantlyderived object position data from a plurality of electronic imagescaptured from a plurality of positions of said electronic imager imagingintersections of objects with a plurality of planar structured lightpatterns, to produce a three-dimensional representation of objectswithin a volume of interest which has less position-dependent positionerror than a three-dimensional representation derived from a singleposition of said electronic imager.